The present invention relates to a disc brake device for keeping a vehicle stationary when parked.
Disc brake devices for keeping vehicles stationary when parked are already known, these being, for example, such as those described in Document WO02/44582. An arm, which pivots under the action of a cable connected to the handbrake, causes a mobile plate to pivot in such a way as to push it toward the brake disc.
Such devices are not designed to apply the parking brake by depressing the service brake pedal, in other words by using hydraulic fluid rather than a cable or some other mechanical means.
The use of a hydraulic fluid to apply a parking brake presents a number of difficulties which stem from the expansion of the parts when applied hot. Document U.S. Pat. No. 6,659,236 proposes to overcome these difficulties by means of a spring which gradually relaxes as the system cools. It then becomes necessary to add, to the fluid pressure customary in applying the brake, an additional pressure for compressing the spring so that the relaxed spring continues to apply a force of a same order of magnitude as that obtained with a customary fluid pressure at the time of brake application. This additional pressure means that the hydraulic circuit has to be over-engineered.
In order to remedy the disadvantages of the known art, the subject of the invention is a disc brake device comprising a piston designed to press a pad against a disc when the piston is subjected to a first force along a first axis in a direction directed from the piston toward the pad. The device is notable in that it comprises a first plate inserted between a first surface of the piston and the pad and designed to generate a second force along the first axis in a direction directed from the pad toward the piston when said pad is caused to move as a result of rotation of the disc.
It is then the potential energy of movement of the vehicle that is used to apply the brake still more firmly. No additional source of energy internal to the braking system is required.
According to the embodiment chosen, the first plate comprises a second surface comprising at least one first line a variable distance away from a plane parallel to said first surface, and the device comprises an element designed to move along said line of the second surface when said pad is made to move as a result of rotation of the disc so that said element moves closer to said first surface; the element is a ball; a second plate comprises a third surface comprising at least one second line a variable distance from a plane parallel to said second surface; said first surface has, passing through it, a rod that has an end designed to follow the movement of the piston when said piston is subjected to said first force along the first axis in a direction oriented from the piston toward the pad, and to be immobilized by a key so as to press the pad against the disc when said piston is no longer subjected to said first force and/or said second force is applied against said end of the rod or alternatively, said second force is applied against said first surface of the piston; said first plate delimits at least one space with oblique boundaries such that pad movement caused by the rotation of the disc tends to increase the separation between said oblique boundaries; said first force is generated by hydraulic fluid pressure applied to the piston; a washer combined with the rod 11 allows the rod to be driven when the washer is subjected to said first force.